5.3 Biomimetic Acoustic Sensors

౪

103

from the frequency separation closely with that of the piezoelectric signals. The same

effect could also be produced with different-length beams on a field-effect transistor as

part of a MEMS acoustic sensor [13].

It is useful to measure vibrations of a variety of wavelengths for an array of medical

applications. For wearable sensors, they have to be made from flexible materials and be

very sensitive. One example uses a network of multiwalled carbon nanotubes (CNT) in a

suspended membrane (Figure 5.7) [14]. The cracks in the MWCNT layer increase flexibil-

ity and change the resistivity, increasing the sensitivity of the sensor (Figure 5.7:(a)i). The

suspension of the membrane allows for larger vibrations and with thus increased sen-

sitivity as well (Figure 5.7:(a)ii). This sensor can be used for a large range of frequencies,

but also for the detection of different arm movement.

Vibration sensors can also be used to measure flow (Figure 5.8) [15]. In this example,

a hair is incorporated into the bilayer interface, and electrodes are fed into each aqueous

phase, resulting in a sensitive flow sensor.

Figure 5.7: (a) Scheme of the layers and set up of the vibration sensor. (i) MVCNT layer with cracks in a sus-

pended membrane (ii) vibration enhancement due to the suspension of the membrane. (b) Sensor output

for a large frequency range. (c) Sensor outputs for arm movement (top) and different sounds (bottom).

With permission from [14].